Road Bike Crank Test

Road Bike Crank Test

As a lot of you tuning in already know, we’ve been working on our in-house road crank tests for the last 7 years, with our updates posted alongside all the previously tested cranks. One thing we’ve come to realize is that while some cranks have obvious changes over the years, others have quietly evolved behind the scenes. Because of this and a desire to build a new testing fixture, particularly one that would handle BB30 cranks as well, we decided it was time to retire the old tests and start again with a clean slate. Please note that because of the new fixture and testing loads, results from this and future tests are not comparable to results from previous tests. Being that only 2 of the first 12 cranks tested in the last round carry over from previous tests we felt this was a good time to make the change.

Luckily, Jason Krantz is back as our resident data-cruncher (Jason is an experienced mechanical engineer with a strong background in both finite element analysis and composite materials.) We’re always happy to have him work with us on our tests and place a high value on his contributions.

Disclaimer: A lot of typing and numbers have gone into this article and we apologize in advance for any typos, but would warn that the possibility of mistakes is present.

About the testing method: Each arm was preloaded with 50 lbs of weight, then all calipers and load cells were zeroed out. Another 150 lbs was added and the difference was measured in mm. Each arm was tested three times and an average of those measurements is the result. A lower number represents a stiffer crank. These will be labeled as Deflection-D(Drive side deflection) and Deflection-ND(non-drive side deflection) . This method uses a total load of 200 pounds, in comparison to the old test which used a total load of 250 pounds. Further more in previous tests a large solid rod was used to simulate the pedal and load was applied 60mm from crank arm. With the new fixture, we’ve switched to using actual steel pedal spindles removed from a set of production pedals. The loading has also been moved slightly inward toward the crank arm.

Notes about stiffness: According to conventional wisdom, the more pedaling stiffness the better. Stiffness implies efficiency, along with the notion of a stiffer bike inspiring confident and responsive handling. As desirable as those traits are, and even after a crank’s stiffness is proven empirically, the outcome still seems subjective—we are simply going by how many people feel more efficient on a bike with a stiff drivetrain. But it’s far from clear whether that tactile, from-my-quads-directly-to-the-road sensation is actually faster. This is the question: is a stiffer drivetrain actually more efficient, or does it just feel that way? Looking at the numbers, we can see that average deflections range from roughly 0.20 inches to 0.30 inches. From this, we can generalize and say that the most flexible crank is about 50% more flexible than the stiffest crank. It’s easy to imagine that the stiffer cranks feel better, or have better “power transfer,” which is a particularly vague and ill-defined concept.

So how can we move beyond “feel” and attempt to quantify whether a stiffer crank is better? The answer is, strain energy. Strain energy is simply the energy stored by an object as it is loaded. Quantifying how much energy stored by a given spring under a particular load is a basic problem that works perfectly well for understanding whether a stiff bicycle crank is better than a slightly less stiff crank. That is, you can think of a bicycle crank as a very stiff, oddly-shaped spring. The equations for calculating stored energy in a beam under bending are fairly simple. The following figure is taken from a Creative Commons-licensed engineering textbook by Piaras Kelly at the University of Auckland:In the equation above, U is strain energy, M is applied moment (torque), L is beam length, E is the Young’s modulus (stiffness) of the beam material, and I is the moment of inertia of the beam cross-section. A crank is somewhat beam-like, but it’s not really a beam. And we’re not applying a pure moment but rather a force at a distance that creates a moment. This bending example is somewhat close, but it’s still not a very good approximation of a crank on a bicycle. We can get a very good approximation of a crank on a bicycle by using finite element analysis (FEA). To find out how much strain energy a typical crank stores, we can solve an FEA model to find the strain energy of each of the constituent elements. We can then add up all of those strain energies to get the strain energy of the whole crank. This strain energy can then be converted into absorbed power by assuming a cadence; we used 100 RPM for this example. In this way, we can determine exactly how much power goes into crank flex, which can then tell us how much crank flex matters to total power output. We used ANSYS, a well-regarded FEA program, to model a generic aluminum left crankarm (172.5mm) and half an attached 24mm steel bottom bracket spindle.The remote force works out to 250 pounds of force (lbf), and it is applied 60mm to the outside of the center of the pedal threads. This simulates applying the force through a pedal.

Most of the action is happening on the inside of the crank; the interior elements report a higher strain energy value than the external ones do. But things get a lot more interesting when we dump the strain energy values for each of the elements to a spreadsheet. By summing the elements’ strain energy values, we can get the total strain energy for the entire crank and half BB spindle. The total strain energy of this crank under a 250-lb pedaling load is 4.604 Joules. As a unit, Joules don’t do much for most cyclists. We can convert them to a more useful unit by assuming a cadence of 100 RPM. At that cadence, this half-crank soaks up 7.67 Watts. The right-hand crank is usually stiffer than its left-hand counterpart, so it stores correspondingly less strain energy. So rather than doubling the left-hand figure, we’ll round down a bit to 14 Watts for the entire crank/BB axle system. 14 Watts might sound like a lot, and it is. But let’s keep in mind that this is a 250-lb force applied 1.67 times per second. A rider applying this force over 160 degrees of crank rotation produces an average power of 880 Watts, which few of us can sustain for long. And 14 Watts out of 880 is 1.6% To put this in perspective, if you were pedaling along at a steady 300 Watts, your crank would be absorbing 4.8 Watts of your effort. But those 4.8 Watts go into winding up your crank “spring,” which will spring back with nearly all the energy that was spent winding it up. Some of that spring-back energy probably helps turn the drivetrain while some of it may behave in a negative manner. However, there’s a fair amount of debate about how much energy is returned. The answer to the energy-return question involves kinematic analysis far outside the scope of this article. For now, we’ll assume that all of those 4.8 Watts spring back in a way that doesn’t help turn the drivetrain nor hinder it. As mentioned before, the most flexible crank in this review shows about 50% more deflection than the stiffest crank. Our FEA crank is quite flexible, and it absorbs 4.8 Watts of a 300-watt effort. Strain energy, roughly speaking, is inversely proportional to stiffness. We can use these relationships to calculate that at 300 Watts, our flexible crank absorbs 4.8 Watts, or 1.6% of total power output. Meanwhile, a 50% stiffer crank absorbs 3.2 Watts, or 1.07%, in strain energy (technically, strain power). That’s a difference of 1.6 Watts (or 4.7 watts at our tested 880 Watts). And remember, this assumes that no strain energy is returned to the drivetrain. That’s not to say that crank stiffness is irrelevant, there is a measurable difference. It also provides all the psychological and “feel” benefits described at the beginning of this section. A stiff crank also incrementally improves efficiency by keeping bearings aligned, keeping the pedals more directly beneath your feet, etc. Keep in mind that this 1.6% calculated strain energy absorption represents an upper bound of energy dissipation—that is, the maximum possible energy loss due to crank flexure. Real cranks are much stiffer than our modeled crank and therefore store less strain energy. Moreover, a great deal of that stored strain energy is likely returned to the drivetrain. The real-world losses to crank flexure are, in all likelihood, a fraction of that number.

Things get slightly more complicated for carbon cranks. Composite materials really do damp vibrations better than most metals, and cyclists treasure this property to ease their stinging hands as they hammer over Belgian cobbles and hop curbs on their way to the local coffee shop. But damping is just another word for energy absorption, and a carbon crank certainly absorbs and dissipates more energy than a metallic crank. Modeling that dissipation requires, among other things, intimate knowledge of the crank’s construction (“laminate schedule,” in the argot of composites engineering) But even if we can’t quantify carbon crank losses due to damping, are they worth worrying about? Almost certainly not. They are a tiny addition to the already-small losses in a metallic crank.

Notes about Crank Length: Over the years a lot of different arguments have been made about the benefits of longer/shorter cranks. None of which has really been thoroughly tested until Jim Martins study. Martin showed that length didn’t statistically matter when it came to power, once power was averaged around the entire pedal circle and not just in the forward position, it turns out that shorter cranks (down to 145mm) produced more average power than a longer crank. This conclusion however considers only average power and not other factors which definitely have a bearing on real world use. Damon Rinard followed up the Martin study with some of his own testing comparing the aerodynamic differences in crank length. In almost every case there was an aerodynamic improvement with the shorter crank and without a loss in power. So the power advantage and aerodynamic advantage, combined with shorter cranks generally allowing for a more aggressive or more comfortable position on the bike and less chance of repetitive motion injury we feel that shorter cranks are something most people should consider. We’re not saying they’re right for everyone, but if you’re on the fence as to which size is best for you, we suggest that you go for the shorter. If you’re interested in more on crank length we suggest reading the above articles as well as this article written by Frank Day for USA Cycling.

Notes about weight: Some cranks claimed weights include rings and bb in their complete weights while others do not. To have a level and fair comparison all cranks in this test will be tested and weighed with their stock bsa bottom brackets, and any crank that does not include rings will use our Praxis rings and KCNC alloy chainring bolts.

Notes on prices: Prices are MSRP for the U.S. and include rings and bottom bracket.

We do plan on adding more cranks to the review as they are released and as testing is completed. In choosing the cranks to start the new review with we listened to feedback from previous tests. We went with the most popular cranks as well as some of the lightest options. One suggestion that kept coming up in past tests was that people wanted to see how an older square taper crank did, so in this test we’ve included one.

Note that in comparison to square taper all the external-cup type cranks are worlds stiffer.

Now Onto the Results

*You’re viewing a truncated table since we can’t fit all the data on a cell phone screen. To see all nine columns and eight data points we collected on every crank please re-visit our site on a desktop or laptop.

Manufacturer

Model

Weight (g)

Price (USD)

Spindle (mm)

Deflection-D (mm)

Deflection-ND (mm)

Average Deflection (mm)

S/W

Campagnolo

Record (2006)

894.7

Not current model

Square Taper

5.60

8.82

7.21

1.550

Campagnolo

Comp Ultra (2015)

669.8

1050

30

4.15

6.66

5.40

2.764

Campagnolo

Record UT Carbon (2014)

674.8

756

25

4.3

7.04

5.67

2.615

Campagnolo

Super Record (2015)

678.3

1165

25

4.1

6.9

5.5

2.680

Cannondale

SISL2** (2014)

609.4

1185

30

4.25

6.91

5.58

2.943

FSA

Kforce Lite (2015)

672.3

699

30

4.24

6.56

5.42

2.747

FSA

SL-K Light (2015)

651.6

649

30

4.33

6.7

5.51

2.784

Lightning

Lightning Carbon (2015)

548.2

860

30

5.5

7.22

6.36

2.870

Praxis

Zayante (2015)

828.8

349

30

3.96

6.17

5.06

2.383

Shimano

Dura Ace 9000 (2014)

698.0

640

24

3.98

7.67

5.83

2.460

Specialized

SWorks** (2015)

663.2

665

30

4.26

5.75

5.01

3.013

Sram

Force22 (2014)

782.3

390

24

4.32

6.99

5.65

2.261

Sram

Red22 (2014)

667.4

490

24

4.08

6.8

5.44

2.754

Thm

Clavicula Classic (2014)

540.8

1550

30

4.39

6.46

5.42

3.410

Thm

Clavicula M3 (2014)

579.9

1250

30

4.65

6.96

5.80

2.972

** Fits only BB30/PF30 frames.

Graphs? Yeah, sure, why not?

Thoughts on Each Crankset

Campagnolo Record (2006) Square Taper Alloy

Complete Weight: 894.7 Grams

Price: Not current model

Spindle: Square Taper

Deflection-D: 8.18 mm

Deflection-ND: 12.60 mm

Average Deflection: 10.39 mm

S/W: 1.076

The Campagnolo Record square taper crank was considered to be one of the top cranksets for many years. We’ve included it in this test just for comparison’s sake. The results were pretty dramatic, revealing the differences between this crank and all the other tested cranks. It was significantly heavier than all the other cranks and at the same time not nearly as stiff. This of course resulted in it having the worst stiffness to weight of any crank in the test.

Campagnolo Record UT Carbon (2014)

Complete Weight: 674.8 Grams

Price: $756

Spindle: 25 mm

Deflection-D: 4.3 mm

Deflection-ND: 7.04 mm

Average Deflection: 5.67 mm

S/W: 2.615

The Campagnolo Record UT crank ranks better than mid-field in pretty much across the board. 10th out of 15 in terms of weight. 11th in deflection and 11th out of 15 in stiffness to weight. A nice looking crank with good shift qualities. BB variations in the past left something to be desired with the PF30 BB version having migration problems, but with the introduction of the Overtorque model this is no longer as big of a concern. My opinion of the non-standard bcd of the 5th bolt still hasn’t changed and I find it quite annoying, as it does seem to be more about removing compatibility with aftermarket rings than improving performance. Overall though this still a very nice crank.

Campagnolo Comp Ultra (2015)

Complete Weight: 669.8 Grams

Price: $1050

Spindle: 30 mm

Deflection-D: 4.15 mm

Deflection-ND: 6.66 mm

Average Deflection: 5.4 mm

S/W: 2.764

The Comp Ultra is Campagnolo’s foray into a 30mm spindle crank and was done quite successfully. They opted to go with a universal 386 design rather than a restricted BB30. The Comp finished mid field in weight, slightly lighter than the other tested Campag cranks. In terms of deflection it was 3rd out of 15 which landed its stiffness to weight at 7th overall. The Comp Ultra has a wide range of bb options including bsa. The biggest drawback to it is that it doesn’t have the same simple installation as the UT cranks and does require special tools for installation and removal.

Campagnolo Super Record (2015)

Complete Weight: 678.3 Grams

Price: 1165

Spindle: 25 mm

Deflection-D: 4.1 mm

Deflection-ND: 6.9 mm

Average Deflection: 5.5 mm

S/W: 2.680

We had hoped to see a bigger change with the new Super Record from the previous Record UT, but it just wasn’t the case. Weight, deflection and stiffness to weight were all almost identical to the results from the UT Record crank. This crank has a more polarizing look, for most people it’s either love it or hate it. The new spider and chainrings do however seem to make a difference in shift quality. So all things being equal this crank is an improvement.

Cannondale SISL2 (2015)

Complete Weight: 609.4 Grams

Price: $1185

Spindle: 30 mm

Deflection-D: 4.25 mm

Deflection-ND: 6.91 mm

Average Deflection: 5.58 mm

S/W: 2.943

The SISL has been the most requested crank for us to test so needless to say we were excited to see how it would do. Of course we already knew the crank was light, at 609 grams it was the 4th lightest crank in the test. It was also on the top end of price spectrum. In terms of deflection it ended up just lower than the middle at 9th out of 15 which put its stiffness to weight at 4th. Having a shorter spindle than most other cranks in the test should have improved its weight, which it clearly did. The shorter spindle should also have resulted in better than standard non-drive deflection but in this case we didn’t notice that. The SISL2 is in our opinion one of the nicest looking cranks in the test, particularly with the tested spiderweb chainrings. However being that it is a true bb30 crank its use is restricted to frames with bb30 and pf30 shells only. We’d still love to see them do a 386 version.

FSA K-Force Light (2015)

Complete Weight: 672.3 Grams

Price: $699

Spindle: 30 mm

Deflection-D: 4.24 mm

Deflection-ND: 6.6 mm

Average Deflection: 5.42 mm

S/W: 2.747

For the K-force Light we tested the 386 Evo version with a threaded bsa spindle, 386 has compatibility with every bb standard we can think of except for bb90. Overall the finish on the crank is very nice. In terms of weight it really wasn’t a standout being 9th out of 15. However this extra weight translated to extra stiffness. In deflection testing it finished 4th out of 15. That stiffness helped to lift its stiffness to weight ratio to 9th overall. Shift quality has definitely improved over the years as has the finish and build quality. Considering its $600 price tag ($699 with ceramic bb) and that it is also available in a Campag specific version, it’s definitely a well rounded crank.

FSA SL-K Light (2015)

Complete Weight: 651.6 Grams

Price: $649

Spindle: 30 mm

Deflection-D: 4.33 mm

Deflection-ND: 6.7 mm

Average Deflection: 5.51 mm

S/W: 2.784

The SL-K takes the K-force up a level. Being 20 grams lighter the SL-K was the 5th lightest crank we’ve tested so far. Deflection suffered a little from the K-force putting this one at 8th out of 15. Overall stiffness to weight ratio was up to 6th overall. Same nice build quality, good selection of lengths (165+) and good looks as the K-force and with rings that shift very well. Also like the K-force this SL-K is a 386 Evo standard which gives it compatibility with just about every bottom bracket standard on the market.

Lightning Cycle Dynamics (2015)

Complete Weight: 548.2 Grams

Price: $860

Spindle: 30 mm

Deflection-D: 5.5 mm

Deflection-ND: 7.22 mm

Average Deflection: 6.36 mm

S/W: 2.870

While this current Lightning crank may look the same as past versions there are definitely some differences with it. Surprisingly when looking at just arms/spider, this is the lightest crank in the test. In the past it was close to the Clavicula weight but we’d never seen it dip under. This version is 6 grams lighter than the THM. However the THM is lighter as a full system because the bb is lighter. But with other cups than the BSA (as tested here), this would be the lightest. The weight savings does come at the cost of stiffness though, with the Lighting being the least stiff (with exception of the square taper Campag) but not by a large margin. The crank is quite light though which gives it the 5th best stiffness to weight ratio of all tested cranks (though two that finished ahead of it are BB30 only). BB options are as wide as a 24mm crank: BSA, Italian, BB86, PF30, BB30, Bbright, BB386, and even BB90. Crank options are also the most plentiful of all tested cranks. Matte or gloss, with or without logos and a variety of arm lengths from 160 up to 190.

Praxis / Turn Zayante (2015)

Complete Weight: 828.8 Grams

Price: $349

Spindle: 30 mm

Deflection-D: 3.96 mm

Deflection-ND: 6.17 mm

Average Deflection: 5.06 mm

S/W: 2.383

The Turn Zayante crank finished the test as the heaviest of all current cranks, but also as the stiffest of all current cranks (with universal fit), and by a respectable margin. Part of the added weight comes from the substantial BB which promises to be extremely durable. Overall this is a very well thought out crank and one that we’d definitely consider as a top choice for training/daily rider crank. Good looks, great shift quality and solid function at a very respectable price. The results of this one make us look forward to what Praxis has planned for their top end crank which we hear will be coming eventually.

Shimano Dura Ace 9000 (2014)

Complete Weight: 698.0 Grams

Price: $640

Spindle: 24 mm

Deflection-D: 3.98 mm

Deflection-ND: 7.67 mm

Average Deflection: 5.83 mm

S/W: 2.46

For many years Dura Ace cranks have been considered the pinnacle of cranks. That may still be the case when it comes to installation, reliability, finish and shift quality. However in the metrics we were measuring in this test the DA 9000 crank fell just short of mid field. 12th of 15 in total weight, 11th of 15 in deflection and 12th in terms of stiffness to weight. The best thing the DA crank has going for it is unrivaled shift quality, which is arguably quite important in a crankset. However it does suffer by adhering to the (now quickly disappearing) 24mm spindle size, and the lack of stock BB options (though aftermarket options are plentiful.) We’d love to see a future update of this crank with a 30mm spindle. The spindle diameter shouldn’t be underestimated. If you look at the drive side test, this crank is the 2nd stiffest of all tested. However when you look at the non-drive side it’s the worst of all the current cranks we’ve tested (excepting the 2006 square taper.)

Specialized SWorks (2015)

Complete Weight: 663.2 Grams

Price: $665

Spindle: 30 mm

Deflection-D: 4.26 mm

Deflection-ND: 5.75 mm

Average Deflection: 5.01 mm

S/W: 3.013

The Sworks crank has done very well in testing. Like the SISL2 the shorter spindle of this crank should help to keep the weight down as well as improve the non-drive side stiffness. In terms of total weight it hits 6th out of 15. Its real quality though is in its stiffness with the best total deflection of any crank we’ve tested to date (as expected it did very well with nds deflection being the only crank to drop below 6mm). Mix those two attributes and the stiffness to weight ratio is great coming in 2nd out of 15. Shift quality is not the best of all the tested cranks but is certainly more than adequate. Finish is very nice as is installation and its unique preload adjuster. The biggest drawback with this crank is the restricted use to only bb30 and pf30 frames. Given its $665 price tag it could be a pretty popular aftermarket crank if it were available in a 386 version.

SRAM Force22 (2014)

Complete Weight: 782.3 Grams

Price: $390

Spindle: 24 mm

Deflection-D: 4.32 mm

Deflection-ND: 6.99 mm

Average Deflection: 5.65 mm

S/W: 2.261

The Force 22 crank is more than 100 grams heavier than Red22 and we expected that to translate into increased stiffness
but in fact it ended up less stiff than the lighter Red22. 10th out of 15 in stiffness and 13th in terms of weight put the
stiffness to weight near the lowest of all the current modern cranks in the test so far. That said, it is still
significantly better in every category than the traditional square taper. It is a good looking crank, better than Red22 in our opinion, but with it being only slightly less expensive we feel the Red22 would be a better choice for most riders looking for a SRAM crank.

SRAM Red22 (2014)

Complete Weight: 667.4 Grams

Price: $490

Spindle: 24 mm

Deflection-D: 4.08 mm

Deflection-ND: 6.8 mm

Average Deflection: 5.44 mm

S/W: 2.754

SRAM’s flagship universal fit crank Red22 comes in as one of the lighter cranks in the test, 7th of 15 and 6th in
deflection which puts its stiffness to weight right in the middle at 8th. Good shift quality, light weight,
reasonable stiffness, wide selection of stock and aftermarket BBs, and the best price of any flagship model in the
test–to us that means that this could be one of the most well rounded cranks available and a good fit for many
riders. The hidden bolt design does restrict some aftermarket chainring compatibility, but overall SRAM has to be
considered as a serious contender with this crank.

THM Clavicula Classic (2014)

Complete Weight: 540.8 Grams

Price: $1550

Spindle: 30 mm

Deflection-D: 4.39 mm

Deflection-ND: 6.46 mm

Average Deflection: 5.42 mm

S/W: 3.410

THM’s Clavicula is now in its 10th year of development and refinement, and it shows. 1st in weight, 5th in stiffness
and 1st in stiffness to weight. Of course that performance comes at a cost, and in this case that cost is not
insignificant. Great aesthetic qualities and a wide range of BB choices (everything except BB90). It does lack in
length options being available only in 170, 172.5 and 175 but given that those are the sizes most people ride it
definitely covers the largest percentage of users. In recent years the weight limit has been increased to 231 pounds
which should cover most riders.

Thm Clavicula M3 (2014)

Complete Weight: 579.9 Grams

Price: $1250

Spindle: 30 mm

Deflection-D: 4.65 mm

Deflection-ND: 6.96 mm

Average Deflection: 5.80 mm

S/W: 2.972

The Clavicula M3 is a newer model than the Classic, designed to be a little heavier and a bit more modular in its
design. 3rd in total weight and 3rd in stiffness to weight (with one ahead of it being a bb30) puts this up with the
best cranks. Unlike the Classic, the M3 uses a removable spider that can be swapped from standard to compact as well as
SRM Powermeters. It has a narrower q-factor than the Classic and a higher weight limit (242 pounds). Its alloy
spindle also gives it more flexibility in BB choices including direct fit plus a lower price, though the M3 is still one of the
most expensive cranks available.

Final Thoughts

Now that you’ve gotten through the entire test, or skipped to the end, we suppose you’re looking for a summary. Well, we aren’t really going to offer much other than to say that when it comes to cycling there really isn’t a universal best. There is a best for a given set of circumstances. Each rider has to decide the aspects that are important for them and their needs, be it weight, aesthetics, price, size, BB compatibility etc… Hopefully we’ve provided enough information to help each rider determine which crank is best for them.

61 Comments

Seb LloydNovember 25, 2014 @ 17:47

Thanks a lot for this article, not only a great read but you explain it all really well.
In my dissertation I am testing the power loss from seat post flex/ deflection during a pedal stroke, could I use the strain energy and convert that to Watts as well?
Cheers Seb Lloyd

Jason KrantzNovember 25, 2014 @ 21:15

Seb, what is your field?
Strain energy would be one way to get at this, I suppose. What losses do you think happen in the seat and seatpost? If I understood better what you're trying to measure, I could give a more informed response.
Cheers,
Jason

Jim GNovember 25, 2014 @ 18:17

Why did you use the 24mm GXP version for the Sram Red and Force cranksets rather than the 30MM spindle? It's clear that the 30MM spindle versions are lighter and presumably stiffer so why GXP? Also, what about Cannondale's hollowgram crank which claims to have the best stiffness to weight ratio of all the major brands?

MadcowNovember 25, 2014 @ 20:06

Jim, our fixture mounts using a bsa bb and the Sram bb30 crank cannot be mounted in a bsa shell. We went with bsa because of universal compatability. That is the crank will fit on any frame not just bb30/pf30 frames. We are planning a future test of bb30 cranks though.

MadcowJanuary 14, 2015 @ 15:07

CraigNovember 26, 2014 @ 06:35

Great test. Interesting how every crank's NDS deflects more than the 06 Record DS. Everyone would say they can detect the stiffness difference between their modern crank and the 06 Record, yet no one complains about NDS stiffness!

MadcowNovember 26, 2014 @ 14:21

FranciscoFebruary 13, 2015 @ 17:54

Madcow, I think you missed Jason's point. He correctly noticed that the NDS deflections of ALL the cranks in this test are larger than the DS deflection of the old square taper 2006 crank. We do not see people claiming that they can feel the difference in stiffness between the left and right sides of their moderns cranks, nor do we see many people complaining that their modern NDS crank is "too flexible". Therefore, it follows that any claims of being able to feel the difference in stiffness between square-taper and modern cranks must be taken with a grain of salt.

Jason KrantzNovember 26, 2014 @ 14:35

If you're concerned about vibration transmitted through the crank, you should get a carbon crank. Because each layer of carbon tries to move relative to its neighbors (interlaminar shear, in engineering-speak) carbon parts damp vibration better than nearly all metal parts. (Parts made of magnesium are a notable exception...magnesium also has outstanding damping properties).
That said, I don't believe I could feel the difference between a carbon and aluminum crank in a blind test. If vibration is a major concern, I'd expect gel shoe insoles would make a much bigger difference than crank material.
Cheers,
Jason

SylvainNovember 26, 2014 @ 15:23

Nice works!
Could you give more detail about your setup? Cyclist applied forces on a pedal which is off-axis to the crank arm. This likely produce a torsion in the arm. Is this important and measurable ?

Jason KrantzNovember 26, 2014 @ 17:17

Sylvain, if you read the article carefully, you'll see that the load is applied through a pedal spindle, which is off-axis to the crank just as in the real world. This does produce a torsional stress in the arm. It is important and it is measurable. If you wanted to distinguish between bending and torsional displacement, you'd just need a second dial gauge applied to the crankarm beneath the pedal eye. This would record bending displacement. Subtracting the bending displacement from the total displacement would give you the torsional displacement.
Fairwheel didn't make this distinction; they measured only combined displacement. In my opinion, that's fine, since the rider will never experience "pure" bending displacement or "pure" torsional displacement independent of one another. If I were designing a new crank, however, I would take both measurements.

MadcowNovember 26, 2014 @ 18:56

RyanNovember 26, 2014 @ 19:10

How about fitting a Rotor ubb30 crank to the praxis bb? I know that I can use it in a 386Evo BB, is the praxis setup the same width or narrower? Would love to use their collet system in a bb30 frame w/ my 3d+.

MadcowNovember 26, 2014 @ 19:45

CHRISNovember 27, 2014 @ 03:20

Hi
nice article.
Wish they would do this type of testing for other bike parts especially frames!
I currently ride sram force 22 and must say your weight result is quite different than mine. My gram scale shows a weight of 715 grams (170mm) for mine. This weight is also confirmed on sram's website (172.5).
So your calculation on s/w should be quite different.
hope this helps!

HammerTimeNovember 27, 2014 @ 13:53

MadcowDecember 1, 2014 @ 13:57

Yes, the new blog will be the replacement for the forum. We felt the there were more than enough forums already available and all we were doing was diluting it further. We will continue to be active and become even more active on Weightweenies, Paceline, velocipede and rbr/mtbr.

ferraristaNovember 29, 2014 @ 16:37

MadcowJanuary 14, 2015 @ 15:04

davidNovember 30, 2014 @ 07:55

Considering the square tapered Campag crank performed the worst of the bunch, what does this say about track cranks? To whit, I see a great trade in Sugino 75s and Shimano 7700s here in LA as though they were forged in the blood of Christ, but from my experience on the road side of things, it baffles me that they would be better than, say, SRAM Omnium or some such.
Would that bear out? I don't doubt that much of this is silly fixie "it's NJS" stuff, but thats judgemental not science.

henryDecember 22, 2014 @ 16:16

There's the bearing drag-loss issue for the track.
with a 7700 BB or a cup and cone SqT BB (sugino superlap) you can remove all the seals and get the BB to spin very very nicely - this lack of seals doesn't matter indoors, and as you are always taking your chain off etc. it is pretty obvious that you are losing something to bearing drag (whether this makes up what you lose in stiffness- who knows?) - bear in mind you are pedalling (and so your cranks are spinning) - very fast - 150-160rpm for sprinters at full speed so the bearing s are going faster than a road sprinter (~120-130 rpm??) and also this higher cadence means that the forces (torques) are lower for a given power
when you try to set up an omnium crank the (stock) BB is much worse and you only get 3-4 (unloaded no chain) spins out of it wheras the 7700 you get more than ten
also steel 24mm spindle versus octalink ~22mm is not such a huge difference and the spindle itself is shorter (shorter tube - less rotational flex)

ian spivackNovember 30, 2014 @ 13:15

Hi,
It seems like a big assumption when you state that " For now, we’ll assume that all of those 4.8 Watts spring back in a way that doesn’t help turn the drivetrain nor hinder it."
Have you considered performing a test to measure elastic hysteresis loss?
http://en.wikipedia.org/wiki/Hysteresis
That might be the best way to quantify how each crankset compares with power loss. This might be a hard test to perform as you would have to do a few measurements on each crankset at different loads, and then measure deflection at each load.
Eitherway, glad to see some sort of quantification/measurement of bike equipment as qualitative analysis seems to be the dominant sales mechanism in the bike industry.
Ian

Jason KrantzDecember 1, 2014 @ 18:21

Yes, Ian, we have in fact considered hysteresis losses. For aluminum cranks, they are effectively nonexistent. Get ready for a tsunami of engineering and material science jargon:
Hysteresis in most HILE materials (Homogenous Isotropic Linear Elastic, a group which includes most metals and their alloys) is extremely low. It's so low, it would be difficult to measure with a lab full of instruments, let alone the single load cell that Fairwheel is using. So it's entirely reasonable to neglect them in our testing and calculations.
Moreover, all aluminum cranks will have the same hysteresis losses (normalized for each crank's stored strain energy). So not only are the hysteresis losses infinitesimal, there's no difference between the losses of a Rotor crank and a 2006 Record crank. (Again, this is as a function of each crank's stored strain energy. If the Rotor crank lost 0.0000002% of its strain energy to hysteresis, the '06 Record crank would also lose 0.0000002% of its strain energy to hysteresis).
Now, this isn't true for all metals. Certain shape memory alloys (like titanium alloyed with nickel) have high hysteresis. But these metals are not HILE materials because they are not linear elastic. These alloys are a special case; they are actually changing phase as they strain, which is very exotic. Nearly all alloys used in the bike industry (e.g., 3/2.5 and 6/4 titanium, all aluminum alloys, all steels) do not exhibit these losses. Magnesium, on the other hand, is a rare metal that damps vibration well. Cast iron is also good at damping vibration, which is one reason it's used for machine tool mounts. For some reason, you don't see a lot of cast iron in the bike industry.
As I mentioned in the article, carbon cranks *do* have hysteresis losses due partly to the polymer matrix but mostly to interlaminar shear between the fiber layers. That hysteresis is the reason carbon frames, handlebars, etc., damp vibration better than their metallic analogues.
Fairwheel may one day attempt to measure this by attaching accelerometers to handlebars and "plucking" them to see how quickly they attenuate (damp) vibrations. This measures hysteresis to a degree, but damping is often frequency-dependent. In other words, a frame that soaks up road buzz at 1000-3000 Hz may absorb much less energy from pedaling inputs at 1.5-2 Hz. Damping response to free vibration is worth measuring, but it may not tell us much about how much power your crank (or frame) is absorbing by turning it into heat.
Fun addendum: if you're really worried about hysteresis losses in your crank and you also feel like THM Claviculas are far too cheap, go out and get a custom crank machined from a chunk of amorphous titanium. Amorphous metals (AKA single-crystal metals) have no defined grain structure, so their hysteresis losses are considerably lower than even regular metals. The most well-known brand name in amorphous titanium is Liquid Metal, which has been used occasionally by Apple. Here's a video comparing a bouncing amorphous titanium bearing with a standard titanium bearing:
http://www.youtube.com/watch?v=nOHoRdgx4uA

ian spivackDecember 1, 2014 @ 19:04

Thanks for your explanation. It gave me flashbacks to engineering school. :)
So it seems that the conclusion would be that there is no power loss in the crankset deflecting and stiffness of the crank-arms/spindle would be very hard to detect while riding.
Great article and response, keep up the good work.
Ian

Jason KrantzDecember 1, 2014 @ 21:16

I'm glad you found the explanation useful. Personally, I believe the losses from flexure are vanishingly small, but I haven't said that in my part of the article. I'm trying to restrict myself to what we *know*. I have theories and ideas as to why the losses are so small, but I can't prove them. Most of what I wrote was to establish an upper bound for losses. We know that losses must be equal to or less than the numbers I presented in the write-up. Thanks for the great questions.

FranciscoDecember 1, 2014 @ 23:20

So what happens to energy stored elastically in cranks? This review answers part of the question while intimating that there are several opinions. Jobst Brandt said that a [component] will return elastic energy but that human muscles were not suited to taking it back ('The Bicyle Wheel'). Gary Houchin-Miller demonstrated that pedalling energy stored as frame flex was ultimately delivered to the drivetrain (Bicycle Quarterly Vol. 4, No. 4). Gary's analysis considered however a smooth sinusoidal pattern of muscle force at the cranks; my understanding is that under a nearly square-wave pattern (as in pedalling out of the saddle) elastically stored energy will mostly be lost.

j.harrisDecember 4, 2014 @ 21:02

this is exceedingly interesting, thank you for performing the test. my question/concern has to do with the testing method, specifically, (a.) the way in which the crank is constrained in the testing apparatus, (b.) the method by which the crank/chainring combo is "fixed" during loading, (c.) the exact point at which the measurements are being taken to determine the displacement. I've run a simulation utilizing an approximation of your set-up (from what i can gather from the one picture) and my results are not aligning with your experimental results, and i would like to figure out where the discrepancies are coming from. i have screenshots and part files(Autodesk Inventor, i can export to numerous other formats...) i would be happy to share with mr krantz...

JoeDecember 13, 2014 @ 00:53

Doug Brown JrDecember 14, 2014 @ 17:52

Fantastic test! I was wondering how BB mods would affect a crank's stiffness, especially laterally. For example, I've installed an FSA press-in threaded sleeve with Hawk Racing BB in my "winter" Kestrel Legend in an attempt to give the crank a better foundation to work from. On my "event" bike I'm utilizing the same FSA sleeve with an Enduro XD-15 BB due to the lateral load my Lightning Cranks apply with the adjusting jam nut. Perhaps that is the next area more work needs to be done in instead of trying to get ridiculously light in this all important energy transfer area. Any thoughts? Thanks again.

HenryDecember 22, 2014 @ 16:27

Did you consider including other out-of-stock cranks such as for example dura-ace 7800, or even some older ones such as 7700 (but please with the proper DA bb not the crappy 105 ones) ? I think this would be especially interesting to see whether real progress was made in terms of stiffness - and I would be very surprised if Octalink was not considerably stiffer than square-taper.
Also the main difference that you find saying 30mm aluminium spindles are stiffer than 24mm steel ones is interesting but it terms of the spring energy returned to the drivechain flex in the crank ARMS is unlikely to be returned but that lost in twisting the spindle/axle is pretty likely to be returned
Additionally if you want to test really stiff cranks try the LOOK zed cranks with the 50mm axle (particularly the track version)

MadcowJanuary 14, 2015 @ 15:00

dkrenikFebruary 13, 2015 @ 18:28

Emiliano JordanFebruary 13, 2015 @ 20:32

It will affect the shifting performance. We designed the test so chainrings have a minimal impact on results. Cranks that did not come stock with a chainring all used the same chainrings to minimize and extra influence on the testing.

Wayne SulakJanuary 14, 2015 @ 01:02

Great work comparing cranks. As mentioned in the post, the effect of crank stiffness is unknown. It seems to me that looking at the crank as part of the bike system that all of the cranks might be stiffer than a normal frame under the same load. In other words if a test like yours was done on a bicycle frame clamped at the drop outs (and possibly the handlebars) rather than a static rig would most of the flex be in the frame or the crank?
If the long members of the frame are much easier to flex than the short crank arms, them even the least stiff crank might bend the frame before the crank flexed much at all. If that is the case then the stiffer cranks give little advantage over the cranks that are just stiff enough to make the frame flex.

Emiliano JordanJanuary 14, 2015 @ 20:16

Your point is something we've put a lot of thought into honestly without a very complicated and involved test we couldn't confirm one way or another. One reason we like to test the components individually is that if there is some power to be saved, even if it's small, it could add up over all the components of a bike. Say one or two watts here and there could end up being 10-20 watts over a bike build. The other reason is that crank stiffness could effect shifting performance and this is very important to us.

Daniel ConnellyJanuary 14, 2015 @ 17:52

Excellent work, as always! However, since for the cantilever example work is proportional to moment squared, and since under constant cadence a quasistatic approximation is valid (deflection depends only on moment, not time), and if you assume constant cadence then moment is proportional to power, when scaling from 880 watts to 300 watts does it make sense to scale by constant efficiency (300/880) or would (300/800)^2 make more sense?
The other "usual" comment is STW doesn't make much sense as something you'd necessarily want to optimize, as it produces a perfect result for either infinite stiffness or zero weight, but the performance advantage of going to either of these extremes would still be only modest. But I know you realize this, and the simplicity of it is very attractive, while it still represents the tradeoff between light & stiff.
In any case, I really appreciate these reviews. Fantastic stuff.

Les AkinsJanuary 14, 2015 @ 19:22

With Rotor's UBB (3D+ crankset) and ability to be fit into PF86 and other similar frames, what are the chances of having that combination tested (he asks because he's just purchased that)? Also I am not seeing the results for the Rotor cranks though I see them referred to in the comments section? Thanks for doing this.

Emiliano JordanJanuary 14, 2015 @ 20:08

We're hoping to add more cranks soon including re-adding Rotor cranks. Can't say we'll get your exact combo.
The reason Rotor is gone is that this is a permanent page for our crank review and it gets updated with new info periodically. Since we re-thought our testing methods between V2.1.0 and V2.2.0 we had to retest everything. The problem was we couldn't get two cranks for that test. The rotors included. You can read more about why this happened here.

joeJanuary 14, 2015 @ 20:34

Any idea what the difference is between the same cranks but 24 vs 30 spindle size? For instance Red22 24 vs Red22 30. For what it's worth I am also interested in the results of the Rotor 3D+ (30mm) cranks in the next review.

Daniel ConnellyJanuary 15, 2015 @ 19:13

Spindle size is the #1 factor in the above table for STW results. If you plot, you'll see the 30 mm spindles essentially all rank above the 25 mm spindles (note the crank description says 30 mm for S-Works, while the table says 25 mm: I believe the 30 mm). So I think you always want to go with the 30 mm spindle where possible. The Look crank, with its mutant wide spindle, would do even better.

Jason KrantzJanuary 21, 2015 @ 04:08

Dan's reply is on the money. Torsional stiffness works out to be (pi/4)* r^4, where r = radius. In other words, we're talking about the radius of the bottom bracket spindle raised to the fourth power. This is huge.
Shimano's bottom bracket spindles are typically 24mm. 30 mm spindles (used by Lightning, Race Face, Cannondale and many others) are a significant improvement on 24mm spindles. In my opinion, it's a credit to Shimano that they can make a reasonably stiff crank with a 24-mm spindle at all.
Cheers,
Jason

HeldringJanuary 18, 2015 @ 14:31

Emiliano JordanJanuary 20, 2015 @ 00:24

Bruce ReyesJanuary 21, 2015 @ 12:46

Great article. I have read numerous articles about crank length. One thing never mentioned is foot size. I have a size 14 foot and when I finally put on a 180 length crank on my bike my feet finally felt as if they had room to open up. My peddling opened up and relaxed. To my surprise it was easier to maintain 90 or 100 rpms. Anyway nothing scientific but my experience after 40 years of road biking.

Christian BratinaJanuary 21, 2015 @ 17:12

From my experience a narrower Q Factor is more efficient, especially climbing, than the wide ones on most modern cranks. Please list the Q Factors.
I applaud your noting that we are not sure if a stiffer crank will make you faster than a flexible one, which follows the same question that Bicycle Quarterly tested on frames, where flexible ones are faster. How about doing some power tap testing on a track to decide.

GilbertJanuary 26, 2015 @ 13:53

Emiliano JordanJanuary 26, 2015 @ 17:02

We're working on our Mountain Bike Crank Review right now, then we'll have to see if it makes more sense to tackle something new like MTB Handlebars or add more cranks like this to the Road Crank review. Either way, stay tuned.

JesseFebruary 6, 2015 @ 01:29

Christian BratinaMarch 18, 2015 @ 09:52

You did not but should have addressed reliability. I find the Shimano cranks incredibly ugly was considering an FSA. But then I cam across a lot of stories of their failures. So I looked into Campy, and the same thing. It sickens me that there is so much fad driven equipment on the market. And all the BB designs only make it worse. FSA and Chris King say they use sealed bearings. Bullshit, they are SHIELDED and Chris King says you should clean and repack them semi annually. Phil Wood makes SEALED bearings that never need cleaning and lubrication.